The purpose of this proposal is to elucidate the mechanisms of passive sensitization of basophils and mast cells by IgE antibody and the mechanisms through which antigen-IgE-antibody interaction on the cell surface leads to the release of chemical mediators. 1) in order to localize the structures in human IgE molecules essential for binging with basophil receptors, structural basis for inactivation of IgE by mild reduction and alkylation treatment will be analyzed. Disulfide bond(s) in the Fc portion of E myeloma protein essential for the binding will be located. Possible degradation of three different antigenic determinants in different positions of epsilon chains will be examined after reduction-alkylation treatment. 2) Nature of IgE receptors on human basophils and the recetors on rat mast cells for mouse IgE antibody will be studied. Attempts will be made to purify and characterize receptor molecules. The nature of binding between IgE and receptors will be studied. 3) Relationship between binding of IgE molecules with basophils and "passive sensitization" for antibody- induced histamine release will be studied using E myeloma protein and the antibody specific for the ideotypic antigenic determinants in the molecules. (4) The steps between antigen-antibody interaction on the target cells and subsequent biochemical events in the cells are unknown. In order to get more information on the steps, two approaches will be made. 1) Purified rat mast cells will be sensitized with mouse IgE antibody followed by challenge with antigen. The effect of antigen- cell-bound-antibody reaction on intracellular cyclic AMP, cyclic GMP and on membrane-associated enzymes will be studied. 2) Cap formation of IgE molecules on human basophils will be induced by anti-IgE and possible movement of receptor molecules on the cells will be investigated.